Manufacturing method for a buried circuit structure

ABSTRACT

A manufacturing method for a buried circuit structure includes providing a substrate having at least a trench therein, forming a conductive layer having a top lower than an opening of the trench in the trench, performing a selective metal chemical vapor deposition (CVD) to form a metal layer having a top lower than the substrate in the trench, and forming a protecting layer filling the trench on the metal layer.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a manufacturing method for a buried circuitstructure, and more particularly, to a manufacturing method for a buriedcircuit structure applied with a selective metal chemical vapordeposition (MCVD).

2. Description of the Prior Art

Along with miniaturization and complexity of integrated circuit (IC),the prior art has always devoted itself to scale down the device sizefor fabricating enough devices and constructing efficient circuit withina limited chip surface. Therefore approaches such as buried bit lines,buried word lines, or multilevel-interconnect structures are developedto create and realize three-dimension IC architectures.

Please refer to FIGS. 1-3, which are cross-sectional views illustratinga conventional manufacturing method for buried bit lines. The prior artfirst provides a substrate 100 having devices (not shown) formedtherein. Then, a plurality of trenches 104 is formed in the substrate100 and followed by forming a contact window (not shown) in each trench104. A first metal layer 108 serving as a buried bit line issubsequently formed in the trench 104. Then, the trenches 104 are filledby an insulating layer and followed by forming a patterned hard mask 102on the substrate 100. The pattern hard mask 102 is formed to define aplurality of trenches 106 having an extension direction perpendicular toan extension direction of the trenches 104. After forming the trenches106, an insulating layer 110 is formed to cover the first metal layer108 exposed in a bottom of the trenches 106, and followed by forming asecond metal layer 112 such as a tungsten layer in the trenches 106.Subsequently, a silicon oxide layer 114 is formed in the trenches 106and on the substrate 100. As shown in FIG. 1, the silicon oxide layer114 covers the second metal layer 112.

Please refer to FIG. 2 and FIG. 3. After forming the silicon oxide layer114, an etching back process is performed to remove a portion of thesilicon oxide layer 114 in the trenches 106 to form a silicon oxidespacer on sidewalls of each trench 106. The silicon oxide spacer 116covers at least a portion of the second metal layer 112 for defining aposition and thickness of the buried bit line formed afterwards. Afterforming the silicon oxide spacers 116, an etching process is performedto remove the second metal layer 112 not covered by the silicon oxidespacers 116, and thus a metal layer 118 is obtained on two oppositesidewalls of the trenches 106, respectively. The metal layer 118 servesas a buried bit line, respectively. Thereafter, a protecting layer (notshown) is formed in the trenches 106 for filling the trenches 106 andthe fabrications of the buried word lines and the buried bit lines areaccomplished.

Please still refer to FIG. 2. It is noteworthy that the second metallayer 112 is a layer having a substantial thickness; therefore it isdifficult to perform the etching process to remove the second metallayer 112 precisely. In the case that the second metal layer 112 is notetched completely, the final metal layers 118 as shown in FIG. 3 maycontact each other at the bottom of the trench 106. Accordingly, buriedbit line short circuit is occurred. On the contrary, in the case thatthe second metal layer 112 is over-etched, the final metal layers 118 asshown in FIG. 3 are undesirably and excessively thinned down.Accordingly, resistance is increased and thus performance of the IC isdeteriorated.

Therefore, the approach that utilizing the silicon oxide spacer 116define the position and the thickness of the buried bit lines havesuffered some disadvantages of complicating process and difficulty withthe process control. Thus, a simplified and economized manufacturingmethod for a buried circuit structure that is able to precisely form theburied circuit structure in the predetermined position is still in need.

SUMMARY OF THE INVENTION

According to an aspect of the present invention, there is provided amanufacturing method for a buried circuit structure. The manufacturingmethod includes providing a substrate having at least a trench formedtherein, forming a conductive layer having a top lower than an openingof the trench in the trench, performing a selective metal chemical vapordeposition (MCVD) to form a metal layer having a surface lower than asurface of the substrate, and forming a protecting layer filling thetrench on the metal layer.

According to the manufacturing method for a buried circuit structureprovided by the present invention, the selective MCVD is utilized toform the metal layer on specific materials but not on the insulatingmaterials. Therefore the etching processes used to form the buriedcircuit structure in the prior art are eliminated from the manufacturingmethod. Accordingly, the process control and cost issues accompaniedwith the etching processes are fundamentally eliminated.

These and other objectives of the present invention will no doubt becomeobvious to those of ordinary skill in the art after reading thefollowing detailed description of the preferred embodiment that isillustrated in the various figures and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1-3 are cross-sectional views illustrating a conventionalmanufacturing method for a buried bit line;

FIGS. 4-8 are drawings illustrating a manufacturing method for a buriedcircuit structure according to a first preferred embodiment provided bythe present invention; and

FIGS. 9-14 are drawings illustrating a manufacturing method for a buriedcircuit structure according to a second preferred embodiment provided bythe present invention; wherein FIG. 9 is a schematic top view of aburied circuit structure, FIGS. 10-14 are cross-sectional views takenalong A-A′ line of FIG. 9, and FIG. 12 is a drawing illustrating amodification to the second preferred embodiment.

DETAILED DESCRIPTION

Please refer to FIGS. 4-8, which are drawings illustrating amanufacturing method for a buried circuit structure according to a firstpreferred embodiment provided by the present invention. As shown FIG. 4,the preferred embodiment first provides a substrate 200 such as asilicon substrate having at least a semiconductor device (not shown)formed therein. Then, a patterned first hard mask 202 is formed on thesubstrate 200. The patterned first hard mask 202 includes insulatingmaterials selected from the group consisting of silicon oxide, plasmaenhanced oxide (PEOX), silicon nitride, silicon oxynitride, siliconcarbide, and combination of these materials. Additionally, the patternedfirst hard mask 202 can be single-layered or a multi-layered structure.Next, an etching process is performed to the substrate 200 through thepatterned first hard mask 202. Consequently, first trenches 210 as shownin FIG. 4 are obtained. Subsequently, a second hard mask 204 coveringsidewalls and bottoms of the first trenches 210 and the patterned firsthard mask 202 is formed on the substrate 200. The second hard mask 204includes insulating materials selected from the group consisting ofsilicon oxide, PEOX, silicon nitride, silicon oxynitride, siliconcarbide, and combination of these materials. Additionally, the secondhard mask 204 can be a single-layered and a multi-layered structure.

Please refer to FIG. 5. Then, a portion of the second hard mask 204 isremoved from the bottoms of the first trenches 210. Consequently, a hardmask spacer 206 is formed on the sidewalls of the first trenches 210.Next, an etching process is performed with the patterned first hard mask202 and the hard mask spacer 206 serving as an etching mask. The etchingprocess is performed to etch the substrate 200 in the bottom of eachfirst trench 210 to a predetermined depth. Accordingly, a second trench212 downwardly extending from the bottom of each first trench 210 isrespectively formed. After forming the second trenches 212, a dielectriclayer 216 is formed on sidewalls and bottoms of the second trenches 212by performing a thermal oxidation process, exemplarily.

Please still refer to FIG. 5. Then, a portion of the dielectric layer216 is removed from the second trench 212. Subsequently, a contactwindow 214 is selectively formed on one of the sidewalls of each secondtrench 212. The contact window 214 is formed to provide electricalconnection between the semiconductor device in the substrate 200 and theburied circuit structure formed afterwards. After forming the contactwindow 214, a conductive layer 218 covering the dielectric layer 216 andthe contact window 214 is formed in the first trenches 210 and thesecond trenches 212. In the preferred embodiment, the conductive layer218 includes titanium nitride (TiN), but not limited to this. Afterforming the conductive layer 218, a patterned photoresist 220 is formedin the second trenches 212. As shown in FIG. 5, the patternedphotoresist 220 covers the conductive layer 218 on the bottoms and thesidewalls of the second trenches 212. Additionally, the top of thepatterned photoresist 220 is preferably higher than the contact window214.

Please refer to FIG. 5 and FIG. 6. Next, an etching process is performedto remove the conductive layer 218 not covered by the patternedphotoresist 220. Then, the patterned photoresist 220 is removed.Consequently, the remained conductive layer 218 has a top lower than anopening of the first trench 210 as shown in FIG. 6. In other words, theconductive layer 218 is remained only in the second trench 212 andcovers the contact window 214.

Please refer to FIG. 7. Subsequently, a selective metal chemical vapordeposition (MCVD) process is performed to the substrate 200. Accordingto the preferred embodiment, the selective MCVD process includes aselective tungsten chemical vapor deposition (W-CVD) 230. The selectiveW-CVD 230 includes a process temperature of 20° C. to 300° C. and aprocess pressure of 30 Pa to 50 Pa. The selective W-CVD 230 furtherincludes introducing tungsten hexafluoride (WF₆), silicon hydride(SiH₄), and nitrogen (N₂). According to the preferred embodiment, a gasflow rate of WF₆ is between 45 standard cubic centimeter per minute(sccm) and 50 sccm, a gas flow rate of SiH₄ is between 20 sccm and 25sccm, and a gas flow rate of N₂ is between 340 sccm and 425 sccm.

It is well-known to those skilled in the art that tungsten can bedeposited on some specific materials such as silicon, aluminum, titaniumnitride, metal materials or conductive materials. According to theselective W-CVD 230 provided by the preferred embodiment, reduction ofWF₆ is occurred at the conductive layer 218 including abovementionedmaterials such as TiN formed on the sidewalls and the bottoms of thesecond trenches 212. In other words, TiN reduces WF₆, thus a tungsten(W) layer is formed (not shown) on the sidewalls and the bottoms of thesecond trenches 212. Due to a self-limiting growth characteristic of theW layer, the W layer formed by the reduction of WF₆ stops growing assoon as the W layer entirely covers the sidewalls and the bottoms of thesecond trenches 212. Then, SiH₄, which is simultaneously introduced withWF₆, is dissociated to SiH_(x) and H, and the quantity of X is from 1-3.Both SiH_(x) and H adsorb on a surface of the conductive layer, namelyon a surface of the W layer. SiH_(x) and H subsequently react with WF₆and thus W and SiHF₃ are formed. Accordingly, W is obtained by thereaction between SiH_(x) and WF₆, and thus is deposited to form a Wlayer 232. It is noteworthy that no reduction is occurred between WF₆and the insulating materials or the dielectric materials while nodissociation of SiH₄ is occurred on surfaces of the insulating materialsor the dielectric materials, either. Therefore, there is no W layer 232formed on areas covered by the insulating or dielectric materials. Inthe preferred embodiment, a surface of the substrate 200 is covered bythe patterned first hard mask 202 and the sidewalls of the firsttrenches 210 are covered by the hard mask spacer 206, therefore siliconmaterials in the substrate 200 and the first trenches 210 are notallowed to be involved in the abovementioned reactions, and thus no Wlayer 232 is formed on the abovementioned surfaces. On the contrary,only the conductive layer 218 in the sidewalls and the bottoms of thesecond trenches 212 are allowed to be involved in the abovementionedreactions, therefore positions where the W layer 232 is preferably anddesirably formed is ensured. In other words, a position or a height ofthe conductive layer 218 decides the position for forming the W layer232. Accordingly, the W layer 232 provided by the preferred embodimentis formed to have a top lower than the opening of the first trench 210,which is lower than the surface of the substrate 200 as shown in FIG. 7.

Please refer to FIG. 8. Thereafter, a protecting layer 234 exemplarilyincluding silicon oxide, silicon nitride or silicon oxynitride is formedto fill the first trenches 210 on the W layer 232. And at least a buriedbit line is obtained. Because the preferred embodiment is applied withthe selective MCVD, no W layer 232 is formed on the surface of thesubstrate 200 that is covered by the patterned first hard mask 202 andon the sidewalls of the first trenches 210 that is covered by the hardmask spacer 206. Furthermore, the formation the conductive layer 218ensures that the W layer 232 is formed on the predetermined anddesirable positions, which is precisely aligned with contact window 214,and thus electrical connection is constructed. Additionally, since theCMP process or etching processes for forming the buried bit linerequired by the prior art are no longer in need. The micro-loadingeffect, which causes different etching results between high and lowdensity patterns and the difficult process control to the etchingprocesses are all prevented.

Please refer to FIGS. 9-14, which are drawings illustrating amanufacturing method for a buried circuit structure according to asecond preferred embodiment provided by the present invention, whereinFIG. 9 is a schematic top view of a buried circuit structure and FIGS.10-14 are cross-sectional views taken along A-A′ line of FIG. 9. It isnoteworthy that in the second preferred embodiment, the steps forforming the buried bit lines are the same with the steps described inthe first preferred embodiment and shown in FIGS. 4-8, therefore thoseidentical elements are designated by the same numerals and the detailsare omitted herein in the interest of brevity.

Please refer to FIG. 9. Those skilled in the art would easily realizethat the word lines and the bit lines are structures perpendicular toeach other as shown in FIG. 9. Therefore, after forming the W layer 232(the buried bit line) in the second trenches 212 and filling the firsttrenches 210 with the protecting layer 234, a photo-etching-process isperformed to form a plurality of third trenches 222 in the substrate200. It is noteworthy that an extension direction of the third trench222 is perpendicular to an extension direction of the buried bit line232 as shown in FIG. 9.

Please refer to FIG. 10. Since the W layer 232 is exposed in a bottom ofthe third trench 222, a protecting layer 236 not completely filling thethird trench 222 is formed to cover sidewalls and bottom of the thirdtrench 222. The protecting layer 236 used to provide electric isolationbetween the buried bit line 232 and the buried word line formedafterwards can include silicon oxide, silicon nitride or siliconoxynitride. Next, a conductive layer 240 such as a doped polysiliconlayer or a TiN layer is formed on the substrate 200 blanketly. As shownin FIG. 10, the conductive layer 240 is formed in the third trench 222and covers the sidewalls and the bottom of the third trench 222. Afterforming the conductive layer 240, a patterned photoresist 242 is formedin the third trench 222. It is noteworthy that a surface of thepatterned photoresist 242 is lower than an opening of the third trench222.

Please refer to FIG. 11. An etching process is subsequently performed tothe conductive layer 240. Consequently, a portion of the conductivelayer 240 not covered by the patterned photoresist 242 is removed. Then,the patterned photoresist 242 is removed and followed by performing adry etching process to remove a portion of the conductive layer 240 fromthe bottom of the third trench 222. Accordingly, the conductive layer240 having a top lower than the opening of the third trench 222 isremained only on the sidewalls of the third trench 222.

Please refer to FIG. 12, which is a drawing illustrating a modificationto the preferred embodiment. As shown in FIG. 12, after forming theconductive layer 240, a dry etching process can be performed to remove aportion of the conductive layer 240 from the bottom of the third trench222 and on the protecting layer 236. Consequently, the conductive layer240 is remained only the sidewalls of the third trench 222. Thereafter,a patterned photoresist 242 having a surface lower than the opening ofthe third trench 222 is formed in the third trench 222. An etchingprocess is subsequently performed to remove the conductive layer 240 notcovered by the patterned photoresist 242. Thus the conductive layer 240having a top lower than the opening of the third trench 222 is remainedonly on the sidewalls of the third trench 222 (shown in FIG. 11). Andthe patterned photoresist 242 is then removed.

Please refer to FIG. 13. A selective MCVD is performed to the substrate200. According to the preferred embodiment, the selective MCVD ispreferably a selective W-CVD 250. A process temperature and a processpressure of the selective W-CVD 250 are the same with the selectiveW-CVD 230 disclosed in the first preferred embodiment; therefore thedetails are omitted for the sake of simplicity. As shown in FIG. 13, theselective W-CVD 250 is performed to form a W layer 252 on the conductivelayer 240 in the third trench 222. As mentioned above, since the W layer252 cannot be formed in the third trench 222 covered by the protectinglayer 236, the W layer 252 is always formed at predetermined anddesirable positions precisely. According to the preferred embodiment, athickness of the W layer 252 is adjustable by adjusting the processduration of the selective W-CVD 250. Therefore the W layer 252 havingpredetermined and desirable thickness is obtained. The W layer 252serves a buried word line/gate, the conductive layer 240 serves as aportion of the word line/gate, and the protecting layer 236 serves as agate dielectric layer.

Please refer to FIG. 14. Thereafter, a protecting layer 254 is formed tofill the third trench 222 on the W layer 252, and thus a buried circuitstructure is obtained. Because the preferred embodiment is applied withthe selective metal CVD, no W layer 232/252 is formed on the surface ofthe substrate 200 and in the third trench 222 that is covered by thepatterned first hard mask 202 and the protecting layer 236. Furthermore,the formation the conductive layer 218 in the second trench 212 and theconductive layer 240 in the third trench 252 ensure the W layer 232 andthe W layer 252 are formed on the predetermined and desirable positions.In other words, the preferred embodiment is to form the buried bit lines232 and the buried word lines 252 at the predetermined and desirablepositions without etching the W layers.

According to the manufacturing method for buried circuit structureprovided by the present invention, the selective CVD is utilized to formthe metal layer on the specific materials but not on the insulatingmaterials. Therefore the etching process and CMP processes used to formthe buried circuit structure in the prior art are eliminated from themanufacturing method. Accordingly, the micro-loading effect usuallyoccurred in the CMP process and the process control and cost issuesaccompanied with the etching processes are all fundamentally eliminated.Furthermore, by adjusting the process parameters and process duration ofthe selective MCVD, a height and thickness of the buried circuitstructure is ensured.

In addition, though the present invention is disclosed with the buriedbit lines and the buried word lines serving as the preferredembodiments, it should be conceivable that the present invention also isperformed to form other buried circuit structures having three-dimensionarchitecture such as the single or dual damascene interconnectstructures. For example, after forming the trenches or vias required bythe single or dual damascene interconnect structure, the conductivelayer or a silicon layer is formed in the trench and/or via forproviding the essential reaction of the selective MCVD. In addition, itis also conceivable to form the trenches or the vias directly in asilicon layer and forming the single or dual interconnect structure byperforming the present invention. And the silicon layer can besubsequently removed to form a single or dual interconnect structurehaving air gap. Furthermore, the present invention can be used to formcapacitor electrode of a trench capacitor or the through-silicon via.

Those skilled in the art will readily observe that numerousmodifications and alterations of the device and method may be made whileretaining the teachings of the invention.

1. A manufacturing method for a buried circuit structure comprising:providing a semiconductor substrate having at least a trench formedtherein, the trench comprising a first trench and a second trench formedin a bottom of the first trench; forming a conductive layer in thesecond trench, the conductive layer having a top lower than an openingof the first trench; performing a selective metal chemical vapordeposition to form a metal layer in the second trench, the metal layerhaving a top lower than a surface of the semiconductor substrate andbeing encompassed by the conductive layer; and forming a protectinglayer filling the trench on the metal layer.
 2. The manufacturing methodfor the buried circuit structure according to claim 1, wherein thetrench is formed by a process that comprises: forming a patterned firsthard mask on the semiconductor substrate; performing a first etchingprocess to etch the semiconductor substrate to form the first trench inthe semiconductor substrate through the patterned first hard mask;forming a second hard mask covering sidewalls of the first trench, thebottom of the first trench, and the patterned first hard mask on thesemiconductor substrate; removing a portion of the second hard mask fromthe bottom of the first trench to form a hard mask spacer on thesidewalls of the first trench; and performing a second etching processto form the second trench in the bottom of the first trench.
 3. Themanufacturing method for the buried circuit structure according to claim2, further comprising: forming a dielectric layer exposing a portion ofsidewalls of the second trench in the second trench; and forming theconductive layer on the dielectric layer in the second trench.
 4. Themanufacturing method for the buried circuit structure according to claim3, further comprising forming a contact window on one of the sidewallsof the second trench after forming the dielectric layer and beforeforming the conductive layer.
 5. The manufacturing method for the buriedcircuit structure according to claim 4, wherein the step of forming theconductive layer further comprises: forming a first conductive layercovering the dielectric layer and the contact window in the first trenchand the second trench; forming a first patterned photoresist coveringthe first conductive layer on the sidewalls and bottom of the secondtrench in the second trench; and removing a portion of the firstconductive layer not covered by the first patterned photoresist layer toform the conductive layer.
 6. The manufacturing method for the buriedcircuit structure according to claim 2, wherein the patterned first hardmask and the second hard mask comprise insulating materials.
 7. Themanufacturing method for the buried circuit structure according to claim6, wherein the insulating materials are selected from the groupconsisting of silicon oxide, plasma enhanced oxide (PEOX), siliconnitride, silicon oxynitride, silicon carbide, and a combination of thesematerials.
 8. The manufacturing method for the buried circuit structureaccording to claim 1, wherein the conductive layer comprises a dopedsilicon layer or a titanium nitride layer.
 9. The manufacturing methodfor the buried circuit structure according to claim 1, wherein theselective metal chemical vapor deposition comprises a selective tungstenchemical vapor deposition (W-CVD).
 10. The manufacturing method for theburied circuit structure according to claim 9, wherein the W-CVDcomprises a process temperature of 20° C. to 300° C.
 11. Themanufacturing method for the buried circuit structure according to claim9, wherein the W-CVD comprises a process pressure of 30 Pa to 50 Pa. 12.The manufacturing method for the buried circuit structure according toclaim 9, wherein the W-CVD further comprises tungsten hexafluoride(WF₆), silicon hydride (SiH₄), and nitrogen (N₂).
 13. The manufacturingmethod for the buried circuit structure according to claim 12, wherein agas flow rate of WF₆ is between 45 sccm and 50 standard cubic centimeterper minute (sccm), a gas flow rate of SiH₄ is between 20 sccm and 25sccm, and a gas flow rate of N₂ is between 340 sccm and 425 sccm. 14.The manufacturing method for the buried circuit structure according toclaim 1, wherein the protecting layer comprises silicon oxide, siliconnitride, or silicon oxynitride.